I recently purchased a flow meter (http://www.adafruit.com/products/828) and hooked it up to my arduino uno. I wrote my own sketch that uses interrupts to count pulses. I tested the sketch with a square wave generator and it counts pulses nicely. I then hooked up the flow sensor to the arduino and used a pump (5 l/min max) to provide a flow rate of ~1.5 L/min (measured by filling a nalgene and a half in one minute. The reported flow rates were WAY off. Something like 2-3x higher than they should be. I then tried the adafruit provided sketch and found that I was still getting flow rates that were way too high (still 2-3ish x). I'm wondering if anyone has looked with a scope at the output pulses here. Has anyone had similar experience with this device? Does anyone know what the rise time of the pulses is (wondering if it's super slow and possibly getting counted twice as a result)? Is there a real datasheet for this product? Thanks a lot!

the flow meters aren't linear with the flow rate - we suggest calibrating them against a known source. So fill up a 5 liter bucket, at the rate you'll be using, then divide out to get liters per pulse (or pulses per meter).